If it's helpful - I had a softopper on a Taco for years. Although I never paid attention to exact speed, I likely had it over 100mph on numerous occasions. The important bit - occasionally it would flap horribly (even at 60 mph) after reinstalling the topper (I took it off and put it on constantly, one of the benefits of these), but I'd just pull over, get inside and tighten down the front (closest to the cab) of the topper, and it would be fine. In other words, how it's installed, and more specifically, how low the roof of the front of the topper sits when compared to the roof of the vehicle, makes all the difference. Conclusion - for me, when I had it tightened down correctly, it was fine at faster speeds (although, as a previous poster also noted, it "sucks in" at high speeds and the framing does appear to look like the ribs showing through the skin on a starving horse). Good luck
